A global position of a mobile user receiver, for example, of a vehicle equipped with a GPS (global positioning system) receiver and determined by a navigation system that is satellite assisted is as a rule subject to accuracy errors. The accuracy errors are caused by atmospheric effects, which result as the consequence of varying propagation speeds of signals transmitted by the navigation system. A global position determined solely by a navigation system is as a rule consequently subject to error.
To reduce the accuracy errors, stationary reference receivers (called base stations) and whose global positions are known are used. A position error of the global position determined by the navigation system can be calculated in the form of correction data and based on the known global position of a reference receiver and the global position of the reference receiver determined by the navigation system. The position error calculated by a stationary reference receiver can then be transmitted to mobile user receivers and used for the correction of global positions of mobile user receivers determined by navigation systems. In the known satellite assisted navigation system, this process is called DGPS (differential GPS).
Stationary reference receivers of this type are, however, not available with blanket coverage. A correction of a global position of a user receiver determined by navigation system is not possible everywhere. Furthermore, the achievable accuracy of a navigation system is dependent on the distance of a mobile user receiver from a stationary reference receiver and thus on the density of reference receivers, i.e. the number of reference receivers per unit of area.